The present invention relates to a catalytic composition for the (co)polymerization of xcex1-olefins.
More specifically, the present invention relates to a catalytic composition based on metallocene complexes which include stabilizing hydrocarbyl groups, and a (co)polymerization process of xcex1-olefins in the presence of said composition.
It is generally known in the art that catalysts with a high activity and selectivity in the polymerization of xcex1-olefins can be obtained by combining an organic oxyderivative of aluminum (in particular, polymeric methylaluminoxane or MAO) with an xcex75-cyclopentadienyl compound (metallocene) of a transition metal of group four of the periodic table of elements (in the form approved by IUPAC and published by xe2x80x9cCRC Press Inc.xe2x80x9d in 1989). There have been numerous publications on the preparation and use of said metallocenes since the eighties; among the first, reference can be made to the description of H. Sinn, W. Kaminsky, in Adv. Organomet. Chem., vol. 18 (1980), page 99 and U.S. Pat. No. 4,542,199.
More recently, catalysts of the metallocene type have been developed, capable of polymerizing olefins also in the absence of organo-oxygenated compounds of aluminum and, in any case, such as to include a lower quantity of metals in the polyolefins thus obtained. Said catalytic systems are normally based on the formation of a catalytic species of a cationic nature, obtained by the contact of a suitable metallocene with an activator consisting of a strong Lewis acid or, more advantageously, an organometallic salt whose anion has a delocalized charge and is slightly coordinative, usually a fluorinated tetra aryl borane. Several cationic systems of this type are described, for example, in the publications of R. R. Jordan in xe2x80x9cAdvances in Organometallic Chemistryxe2x80x9d, vol. 32 (1990), pages 325-387, and of X. Yang et al. in xe2x80x9cJournal of America Chemical Societyxe2x80x9d, vol. 116 (1994), page 10015, where numerous patent references on the matter, are quoted, together with a wide general survey in the field.
Other cationic systems based on metallocene and fluoro aryl aluminates are described in international patent application WO 98/0715, disclosing an enhanced catalytic activity. These catalysts, however, are relatively complex to prepare and are particularly unstable to air and humidity, analogously to those containing boron anions; moreover, they cannot be easily adapted to non-alkylated metallocene complexes.
More recently, the presence of an active catalytic species of the cationic type has also been assumed in polymerization catalysis based on metallocenes and aluminoxanes.
One of the unresolved drawbacks of metallocene catalysts of the ionic type, is the relative complexity of the process for their production, as well as various problems relating to their stability, both for their preservation before use and in relation to the duration of the active species during the polymerization process. It is well known, in fact, that these ionic catalysts can be obtained by the direct reaction of an alkyl-metallocene, such as, for example, dimethyl bis-indenyl zirconium, with a suitable salt including a boron anion with a delocalized charge and a cation capable of extracting an alkyl group bonded to the metallocene and forming a neutral and stable molecule. The use of alkyl metallocenes, however, causes serious problems relating to the preservation and stability of these compounds, and consequently the possibility is known of equally obtaining ionic metallocenes also starting from the respective chlorides, but using an alkyl aluminum to form, in situ, an intermediate alkyl metallocene. This latter method, however, does not allow full utilization of the metallocene compound, which is partially deactivated, and also requires the use of high quantities of metal in the co-catalyst, with a consequent deterioration in the dielectric properties and compatibility with food of the polymeric or hydrogenated products obtained in the presence of said catalysts.
The production of metallocene catalysts for the polymerization of olefins therefore seems to still have significant drawbacks, in spite of the remarkable progress made with respect to the traditional Ziegler-Natta polymerization, and there seem to be considerable margins for further improvement to meet the increasingly refined demands of industry and the market.
Japanese patent application No. 11-165075 describes certain metallocene complexes of a metal of group 4 comprising two styril or oligostyril groups bonded to the metal. Such complexes are used for the catalytic hydrogenation of olefins.
Studies on the structure and synthesis of bis-cyclopentadienyl-allyl complexes of metals of group 4 of the periodic table have been reported in literature, in the publication J. Organomet. Chem., vol. 14, 149-156, (1968) page 150. In this study, a significant instability of said allyl complexes with time, is observed.
Subsequently, Italian patent application nr. MI00A02776, of the Applicant, describes allyl-metallocene complexes of group 4, showing a significantly improved stability and performance reproducibility. The allyl-metallocene complexes described therein, however, also need particular attention during their synthesis and do not have a completely satisfactory versatility in the formation of the desired catalysts.
In the continuous attempt to satisfy the above demands with the development of innovative processes and materials, the Applicant has now found a new group of metallocene complexes with stabilizing hydrocarbyl groups in the molecule, which surprisingly allow catalytic systems to be obtained, which are stable enough to allow their transportation and storage for prolonged periods of time and which are also suitable for the formation of metallocene catalysts with a high activity and stability, combined both with ionizing co-catalysts and with aluminoxanes and other analogous activators.
A first object of the present invention therefore relates to, and is claimed as such, a catalytic composition for the (co)-polymerization of ethylene and other xcex1-olefins, i.e. the homo-polymerization of ethylene and other xcex1-olefins, the copolymerization of ethylene with one or more other monomers copolymerizable therewith, such as, for example, xcex1-olefins, conjugated or non-conjugated diolefins, styrene and its derivatives, etc., the co-polymerization of xcex1-olefins with each other or with other monomers copolymerizable therewith. Said catalytic composition includes a particular metallocene complex, as specified hereunder or the product obtained from the combination (i.e. contact and reaction) of the same with an activator (co-catalyst) selected from those known in the art of metallocene polymerization catalysis, particularly an organic compound of a metal Mxe2x80x3 selected from boron, aluminum, gallium and tin, or a fluorinated derivative of a cyclopentadienyl compound, or a combination of said compounds.
In particular, said catalytic composition includes, according to the present invention, the following two components in contact with each other, or the product of their reaction:
(i) a metallocene complex of a metal M of group 4 of the periodic table, including at least one xcex75-cyclopentadienyl group and at least one unsaturated hydrocarbyl organic group Rxe2x80x2, bonded to the metal M;
(ii) an ionizing activator consisting of at least one organic or organometallic compound capable of reacting with said metallocene complex (i) so as to form a positive ionic charge thereon by the extraction of an anion of an unsaturated hydrocarbylic organic group and formation of a non-coordinating anion with a delocalized ionic charge,
characterized in that said unsaturated hydrocarbyl group Rxe2x80x2 has the following formula (I):
-(AxDyUz)RIxe2x80x83xe2x80x83(I)
wherein:
A represents any monomeric unit deriving from a vinylaromatic group polymerizable by means of anionic polymerization, having from 6 to 20 carbon atoms;
D represents any monomeric unit deriving from a conjugated diolefin polymerizable by means of anionic polymerization, having from 4 to 20 carbon atoms;
U represents any generic optional monomeric unit deriving from an unsaturated compound co-polymerizable with any of the above conjugated diolefins D or vinylaromatic compounds A;
RI represents hydrogen or a hydrocarbyl group having from 1 to 20 carbon atoms,
each index xe2x80x9cxxe2x80x9d and xe2x80x9cyxe2x80x9d can be independently zero or an integer, provided the sum (x+y) is equal to or higher than 2, preferably between 2 and 50, even more preferably between 2 and 25;
xe2x80x9czxe2x80x9d can be zero or an integer ranging from 1 to 20.
Said ionizing activators forming component (ii) are normally known in the art and can be divided into four main groups: I) oxygenated organometallic compounds of the metals of groups 13 and 14 of the periodic table, II) non-coordinating ionic organometallic compounds, III) non-coordinating Lewis acids and IV) poly-fluorinated cyclopentadienyl or cyclohexadienyl compounds. Compounds of the type II), III) and particularly IV) are preferred.
A second object of the invention relates to a process for the (co)polymerization of ethylene or xcex1-olefins, characterized in that it is carried out in the presence of said catalytic composition.
Possible further objects of the present invention will appear evident from the following description and examples.